Agricultural combines have increased in capacity to harvest large quantities of crop material to such a degree that it is becoming desirable to have the capability to increase the ground speed of the combine to match header productivity with the increased combine capacity. Generally, the maximum ground speed of a header is considered to be the greatest speed at which the cutting sickle of the header will not strip and leave crop on the field. This, in turn, is a function of the speed of reciprocating movement of the knife assembly or assemblies of the sickle, which is typically expressed in terms of strokes per minute of the knife assemblies. Generally in this regard, the more strokes per minute of the knife assembly of a sickle, the greater its crop cutting capacity, and thus the greater ground speed achievable using that sickle. However, the maximum achievable strokes per minute of a sickle has been found to be a function of the mass of the knife assembly being moved in the reciprocating manner. Presently, for grain headers having a width of about 40 feet, the sickle will include two knife assemblies having a width of about 20 feet each. For a header of 30 feet, two knife assemblies of about 15 feet each will typically be used. These knife assemblies are typically operated at maximum speeds of up to about 1300 strokes per minute. This translates to a maximum ground speed of about 7 miles per hour without stripping.
In contrast to the above-discussed sickles of grain headers, sickles of some known windrowers can be operated at maximum speeds of up to about 2000 strokes per minute. This provides a correspondingly higher ground speed capability, of approximately 11 miles per hour. However, the knife assemblies of these sickles are relatively short, having maximum widths of only about 9 feet. A windrow sickle utilizing dual knife assembly drives will be twice this length. As a result, these knife assemblies have a mass that is only a fraction of that of a knife assembly of a 30 foot wide grain header, and even less than that of a 40 foot wide header, hence the greater maximum speed achievable.
Presently, the knife assemblies of the known large headers of plant cutting machines are driven from the side or end of the header by an oscillating drive, which can include, but is not limited to, an eccentric shaft on a rotating hub, a wobble drive, or a similar well known commercially available device. This location is advantageous, as it does not obstruct or interfere with flow of cut crop material into the header. However, it also a disadvantage for wider headers, as it requires the knife assemblies to have a length of at least one half the width of the header, and thus a greater mass, which in turn, requires a lower operating speed.
Thus, what is sought is a header of an agricultural cutting machine, such as a combine or windrower, and particularly a wide header 30 feet or more wide, which has a sickle operable at a higher cutting speed of at least about 1600 strokes per minute, to allow harvesting at higher ground speeds, and which overcomes one or more of the shortcomings and disadvantages referenced above.